docs: def reply(self, message):
          """ Sends a reply to this USSD message in the same USSD session 
          
          :raise InvalidStateException: if the USSD session is not active (i.e. it has ended)
          
          :return: The USSD response message/session (as a Ussd object)
          """
          if self.sessionActive:
              return self._gsmModem.sendUssd(message)
          else:
              raise InvalidStateException('USSD session is inactive')